Methods and systems for HARQ protocols

ABSTRACT

Methods described herein are for wireless communication systems. One aspect of the invention is directed to a method for a HARQ process, in which the HARQ process includes a first transmission of an encoder packet and at least one retransmission. The method involves allocating a transmission resource for each respective transmission. The method involves transmitting control information from a base station to a mobile station for each respective transmission. The control information includes information to uniquely identify the HARQ process and an identification of one of a time resource, a frequency resource and a time and frequency resource that is allocated for the transmission. In some embodiments of the invention, specific control information is signalled from a base station to a mobile station to enable RAS-HARQ operation. In some embodiments of the invention, retransmission signaling in included as part of regular unicast signaling used for both first transmission and retransmissions. In some embodiments of the invention, a 3-state acknowledgement channel and associated error recovery operation enables the base station and mobile station to recover from control signaling error and reduce packet loss.

RELATED APPLICATIONS

This application is a continuation U.S. patent application Ser. No.16/706,759, filed Dec. 8, 2019, which is a continuation of U.S. patentapplication Ser. No. 16/004,740, filed Jun. 11, 2018, now U.S. Pat. No.10,686,561, which is a continuation of U.S. patent application Ser. No.15/491,575, filed Apr. 19, 2017, now U.S. Pat. No. 10,009,149, which isa continuation of U.S. patent application Ser. No. 15/168,669, filed May31, 2016, now U.S. Pat. No. 9,654,258, which is a continuation of U.S.patent application Ser. No. 14/918,934, filed Oct. 21, 2015, now U.S.Pat. No. 9,374,198, which is a continuation of U.S. patent applicationSer. No. 14/500,468, filed Sep. 29, 2014, now U.S. Pat. No. 9,197,377,which is a continuation of U.S. patent application Ser. No. 14/012,166,filed Aug. 28, 2013, now U.S. Pat. No. 8,959,410, which is acontinuation of U.S. patent application Ser. No. 12/988,717, filed Oct.20, 2010, now U.S. Pat. No. 8,527,829, which claims the benefit of andis a National Phase Entry of International Application No.PCT/CA2009/000522, filed Apr. 21, 2009, which claims the benefit of U.S.Provisional Patent Application No. 61/046,625 filed on Apr. 21, 2008 andU.S. Provisional Patent Application No. 61/050,329 filed on May 5, 2008,which are hereby incorporated by reference in their entirety.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, any disclaimer made in the instant applicationshould not be read into or against the parent application or otherrelated applications.

FIELD OF THE INVENTION

The invention relates to wireless communication systems.

BACKGROUND OF THE INVENTION

Various wireless access technologies have been proposed or implementedto enable mobile stations to perform communications with other mobilestations or with wired terminals coupled to wired networks. Examples ofwireless access technologies include GSM (Global System for Mobilecommunications) and UMTS (Universal Mobile Telecommunications System)technologies, defined by the Third Generation Partnership Project(3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies,defined by 3GPP2.

As part of the continuing evolution of wireless access technologies toimprove spectral efficiency, to improve services, to lower costs, and soforth, new standards have been proposed. One such new standard is theLong Term Evolution (LTE) standard from 3GPP, which seeks to enhance theUMTS wireless network. The CDMA 2000 wireless access technology from3GPP2 is also evolving. The evolution of CDMA 2000 is referred to as theUltra Mobile Broadband (UMB) access technology, which supportssignificantly higher rates and reduced latencies.

Another type of wireless access technology is the WiMAX (WorldwideInteroperability for Microwave Access) technology. WiMAX is based on theIEEE (Institute of Electrical and Electronics Engineers) 802.16Standard. The WiMAX wireless access technology is designed to providewireless broadband access.

A few variations of hybrid automatic repeat request (HARQ)transmission/operation schemes exist in the above identified accesstechnologies. One variation is unicast HARQ in which each encoded packetincludes data from one user. This can be fully asynchronous in whichcase the modulation and coding scheme (MCS), transmission time(slot/frame) and resource allocation are independent for eachtransmission of an encoded packet (first and all re-transmissions).Assignment signaling is used to describe the resource allocation, MCSand user IDs for each transmission and re-transmission. While thisapproach allows adaptation to real time channel conditions, it incurslarge signaling overhead. Unicast HARQ can alternatively be fullysynchronous. In this case, the MCS scheme for transmissions (first andall retransmissions) is the same, resource allocation (location) remainsthe same for first and all retransmissions (the transmission locationmust be the same as the first transmission). The transmission intervalis fixed, and assignment signaling is required only for the firsttransmission. This enables lower signaling overhead for retransmission,but can cause significant scheduling complexity and signaling overheadfor the first transmission due to the irregular vacancies of resourcesthat occurs since some resources need to be reserved for retransmissionsthat may not be necessary.

Another HARQ variant is multicast HARQ in which each encoded packetincludes data for multiple users. The worst channel quality indicators(CQIs) among multiple users are considered for selecting MCS. The entirepacket is retransmitted if one or more users could not decode itsuccessfully, even though some of the users may have successfullydecoded the packet. Multi-cast HARQ can be implemented using fullyasynchronous and fully synchronous schemes.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a methodcomprising: for a HARQ process, the HARQ process comprising a firsttransmission of an encoder packet and at least one retransmission, inwhich a transmission resource for each respective transmission isallocated; transmitting control information from a base station to amobile station for each respective transmission, the control informationcomprising: information to uniquely identify the HARQ process; and anidentification of one of a time resource, a frequency resource and atime and frequency resource that is allocated for the transmission.

In some embodiments, transmitting information to uniquely identify theHARQ process includes transmitting one of: an encoder packet identifier(ID) to uniquely identify the encoder packet; and a resource identifier(ID) of a previous transmission.

In some embodiments, transmitting control information for the firsttransmission also comprises one or more of: a modulation and codingscheme (MCS) for the encoder packet; a MIMO mode used for transmittingthe encoder packet; and one or more other pieces of control informationrelevant to the HARQ transmission of the encoder packet.

In some embodiments, transmitting control information further comprises:scrambling the control information using a user identifier (ID)associated with the mobile station.

In some embodiments, for allocating a transmission resource for at leastone unicast Uplink (UL) transmission, transmitting control informationcomprises: transmitting a UL control segment that is a portion of a DLtransmission resource, the UL control segment comprising a portion thatidentifies a location in the UL control segment for transmitting unicastcontrol information for each at least one unicast UL transmission and aportion that defines the control information for use in transmitting theunicast UL transmission.

In some embodiments, for allocating a transmission resource for at leastone unicast Downlink (DL) transmission, transmitting control informationcomprises: for each at least one unicast DL transmission, transmitting aDL unicast control and traffic segment comprising a portion of the DLunicast control and traffic segment that defines the control informationfor use in transmitting the unicast DL transmission and a portion of theDL unicast control and traffic segment for transmitting data for therespective unicast DL transmission.

According to a second aspect of the invention, there is provided amethod for acknowledging a DL HARQ transmission comprising: receiving anencoder packet; if the encoder packet is successfully decoded,transmitting an acknowledgement (ACK); if the encoder packet is notsuccessfully decoded, transmitting a negative acknowledgement (NAK); ifno retransmission is received within a predetermined time period oftransmitting the NAK, transmitting a NULL indicating that no controlinformation signalling pertaining to the retransmission has beenreceived.

According to a third aspect of the invention, there is provided a methodfor acknowledging a DL HARQ transmission comprising: if anacknowledgement (ACK) in response to a previously transmitted encoderpacket has been received, not retransmitting an encoder packet; if anegative acknowledgement (NAK) in response to a previously transmittedencoder packet has been received, retransmitting a sub-packet of theencoder packet; if a NULL is received indicating that no controlinformation signalling has been received by a sender of the NULLregarding a previously transmitted encoder packet, retransmitting atleast a sub-packet of the encoder packet.

In some embodiments, retransmitting at least a sub-packet of the encoderpacket if a NULL is received comprises: if the NULL is received inresponse to a previously transmitted sub-packet of an encoder packetthat is a first sub-packet transmission, retransmitting the firstsub-packet transmission, the first sub-packet transmission comprisingcontrol information signaling sent in a first sub-packet transmission;if the NULL is received in response to a previously transmittedsub-packet of an encoder packet that is a subsequent sub-packettransmission to a first sub-packet transmission, retransmitting thesubsequent sub-packet transmission, the subsequent sub-packettransmission comprising control information signaling that comprises:information to uniquely identify the HARQ process; and an identificationof one of a time resource, a frequency resource and a time and frequencyresource that is allocated for the subsequent sub-packet transmission.

In some embodiments, retransmitting control information signalling touniquely identify the HARQ process includes transmitting one of: anencoder packet identifier (ID) to uniquely identify the encoder packet;and a resource identifier (ID) of a previous transmission.

In some embodiments, retransmitting control information signaling sentin the first sub-packet transmission comprises: information to uniquelyidentify the HARQ process; an identification of one of a time resource,a frequency resource and a time and frequency resource that is allocatedfor the transmission; and one or more of: a modulation and coding scheme(MCS) for the encoder packet; a MIMO mode used for transmitting theencoder packet; and one or more other pieces of control informationrelevant to the HARQ transmission of the encoder packet.

According to a fourth aspect of the invention, there is provided amethod for rescheduling a UL HARQ transmission comprising: if an encoderpacket is not successfully decoded, scheduling an UL transmission of asub-packet at a predetermined time interval; and transmitting controlinformation pertaining to the UL transmission according to the firstaspect of the invention described above.

According to a fifth aspect of the invention, there is provided a methodof error recovery for a UL HARQ transmission comprising: if a NULL isreceived in response to a previously transmitted sub-packet of anencoder packet that is a first sub-packet transmission; dynamicallyscheduling a retransmission of the first sub-packet transmission at anytime; retransmitting the first sub-packet transmission, the firstsub-packet transmission comprising control information signaling sent ina first sub-packet transmission; if a NULL is received in response to apreviously transmitted sub-packet of an encoder packet that is asubsequent sub-packet transmission to a first sub-packet transmission;scheduling a retransmission of the first sub-packet transmission at apredetermined time; retransmitting the subsequent sub-packettransmission, the subsequent sub-packet transmission comprising controlsignaling information that comprises: information to uniquely identifythe HARQ process; and an identification of one of a time resource, afrequency resource and a time and frequency resource that is allocatedfor the subsequent sub-packet transmission.

According to a sixth aspect of the invention, there is provided a methodcomprising: in a system having a known HARQ acknowledgement (ACK) delay,retransmit delay and number of HARQ interlaces, which are each definedin configuration signalling sent to a mobile station and which are afunction of at least one of a time division duplexing downlink/uplink(TDD DL/UL) ratio and a frequency division duplexing downlink/uplink(FDD DL/UL) ratio, at a base station, determining the timing forreceiving an ACK/NAK from a mobile station based on configurationsignalling in response to a previously sent transmission of an encoderpacket by the base station; and at a mobile station, determining thetiming for receiving one of a transmission and a retransmission of asub-packet of an encoder packet from a base station based on theconfiguration signalling in response to a previously sent NAK by themobile station.

In some embodiments, the HARQ acknowledgement (ACK) delay,retransmission delay and number of HARQ interlaces, which are eachdefined in configuration signalling sent to a mobile station are afunction of portioning of legacy and non-legacy transmission resources.

In some embodiments, a non-legacy transmission resource is atransmission source supported by at least one of: IEEE802.16m, WiMAXevolution and LTE advanced.

In some embodiments, the ACK/NAK and the transmission andretransmissions can be transmitted on one of: a time resource, afrequency resource, and a time and frequency resource.

In some embodiments, if the TDD DL/UL ratio of sub-frames of a frame areasymmetric; the UL ACKs for corresponding DL transmissions, in which theDL transmissions occur in more DL sub-frames of the frame than ULsub-frames that are available for the UL ACKs, transmitting a pluralityof UL ACKs in one UL sub-frame; the DL ACKs for corresponding ULtransmissions, in which the UL transmissions occur in more UL sub-framesof the frame than DL sub-frames that are available for the DL ACKs,transmitting a plurality of DL ACKs in one DL sub-frame.

In some embodiments, if the FDD DL/UL ratio of sub-frames of a frame areasymmetric; the UL ACKs for corresponding DL transmissions, in which theDL transmissions occur in more DL sub-frames of the frame than ULsub-frames that are available for the UL ACKs, transmitting a pluralityof UL ACKs in one UL sub-frame; the DL ACKs for corresponding ULtransmissions, in which the UL transmissions occur in more UL sub-framesof the frame than DL sub-frames that are available for the DL ACKs,transmitting a plurality of DL ACKs in one DL sub-frame.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theattached drawings in which:

FIG. 1 is a block diagram of a cellular communication system on whichembodiments of the invention may be implemented;

FIG. 2 is a schematic diagram of a transmission resource used forsub-frame control signaling according to an embodiment of the invention;

FIGS. 3A to 3E are example schematic diagrams of radio frame havingdownlink (DL) and uplink (UL) portions for DL transmissions and ULacknowledgements for a HARQ scheme according to an embodiment of theinvention;

FIGS. 4A to 4C are example schematic diagrams of radio frame havingdownlink (DL) and uplink (UL) portions for UL transmissions and DLacknowledgements for a HARQ scheme according to an embodiment of theinvention;

FIG. 5 is a schematic diagram of an example of a resource availabilitybitmap in which group and unicast allocations can coexist according toan embodiment of the invention;

FIG. 6A is a schematic diagram of a conventional packet preparation;

FIG. 6B is a schematic diagram of a packet preparation process forsuperposition of a packet for use in interference cancellation accordingto an embodiment of the invention;

FIG. 7 is a schematic diagram for a system in which a packet preparationprocess is used for superposition of a packet according to an embodimentof the invention;

FIG. 8 is a schematic diagram of sub-carriers of two adjacent carriersthat are not aligned due to the spacing of the respective carriers;

FIG. 9 is a schematic diagram of an example of two adjacent carriers inwhich each carrier supports both legacy and non-legacy sub-frames in atransmission resource according to an embodiment of the invention;

FIG. 10 is a schematic diagram of an example of two adjacent carriers inwhich one carrier supports legacy transmissions and the other carriersupports non-legacy transmissions according to an embodiment of theinvention;

FIG. 11 is a schematic diagram of an example of two adjacent carriers inwhich one carrier supports both legacy and non-legacy sub-frames in atransmission resource and the other carrier supports only non-legacysub-frames in the transmission resource according to an embodiment ofthe invention;

FIGS. 12A and 12B are schematic diagrams of an example of two adjacentcarriers in which both carriers support non-legacy transmissionsaccording to an embodiment of the invention;

FIGS. 13A and 13B are schematic diagrams of an example of two adjacentcarriers in which both carriers support non-legacy transmissionsaccording to another embodiment of the invention;

FIG. 13C is a schematic diagram of an example of multiple adjacentcarriers in which each of the carriers support non-legacy transmissionsaccording to an embodiment of the invention;

FIG. 14 is a schematic diagram of an example of two adjacent carriers inwhich one carrier supports legacy transmissions and the other carriersupports non-legacy transmissions according to an embodiment of theinvention;

FIG. 15 is a block diagram of an example base station that might be usedto implement some embodiments of the present invention;

FIG. 16 is a block diagram of an example wireless terminal that might beused to implement some embodiments of the present invention;

FIG. 17 is a block diagram of a logical breakdown of an example OFDMtransmitter architecture that might be used to implement someembodiments of the present invention;

FIG. 18 is a block diagram of a logical breakdown of an example OFDMreceiver architecture that might be used to implement some embodimentsof the present invention;

FIG. 19 is a flow chart of an example method according to an embodimentof the invention;

FIG. 20 is a flow chart of an example method according to anotherembodiment of the invention;

FIG. 21 is a flow chart of an example method according to yet anotherembodiment of the invention;

FIG. 22 is a flow chart of an example method according to a furtherembodiment of the invention;

FIG. 23 is a flow chart of an example method according to anotherembodiment of the invention;

FIG. 24 is a flow chart of an example method according to a furtherembodiment of the invention; and

FIG. 25 is a flow chart of an example method according to yet anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

For the purpose of providing context for embodiments of the inventionfor use in a communication system, FIG. 1 shows a base stationcontroller (BSC) 10 which controls wireless communications withinmultiple cells 12, which cells are served by corresponding base stations(BS) 14. In general, each base station 14 facilitates communicationsusing OFDM with mobile and/or wireless terminals 16, which are withinthe cell 12 associated with the corresponding base station 14. Themobile terminals 16 may be referred to as users or UE in the descriptionthat follows. The individual cells may have multiple sectors (notshown). The movement of the mobile terminals 16 in relation to the basestations 14 results in significant fluctuation in channel conditions. Asillustrated, the base stations 14 and mobile terminals 16 may includemultiple antennas to provide spatial diversity for communications.

Methods of transmission described herein may be performed for one orboth of uplink (UL) and downlink (DL). UL is transmitting in a directionfrom a mobile station to a base station. DL is transmitting in adirection from the base station to the mobile station.

HARQ Protocol and Timing for Wireless Systems

The TGm SRD (IEEE 802.16m-07/002r4) specifies the followingrequirements:

in section 6.2.1 pertaining to Data latency, Table 3 defines a maximumallowable latency for DL and UL of 10 ms; and

in section 6.10 pertaining to System overhead it is defined that“Overhead, including overhead for control signaling as well as overheadrelated to bearer data transfer, for all applications shall be reducedas far as feasible without compromising overall performance and ensuringproper support of systems features”.

Aspects of the invention provide a HARQ scheme to address aspects of theabove requirements. However, while aspects of the invention may bedescribed in regard to IEEE802.16m, it is to be understood thatembodiments of the invention are not limited to IEEE802.16m. Someembodiments of the invention may be applied to other communicationstandards as well, such as, but not limited to WiMAX evolution and LTEadvanced.

Described herein are embodiments for use with HARQ schemes. Someembodiments of the invention involve a resource adaptive HARQ (RAS-HARQ)scheme, in particular control signaling for the RAS-HARQ scheme.RAS-HARQ provides a trade-off between signaling overhead and flexibilityin resource multiplexing among users. In some embodiments of theinvention, specific control information is signalled from a base stationto a mobile station to enable RAS-HARQ operation.

In some embodiments of the invention, retransmission signaling inincluded as part of regular unicast signaling used for both firsttransmission and retransmissions.

Synchronous HARQ has the benefit of minimum signaling overhead asretransmission does not need to be signaled, but the drawback ofInflexible resource allocation and multiplexing. If the mobile stationmisses the control signaling of first sub-packet and base station doesnot recognize that, it is not possible to recover the packet. In case ofACK to NAK error in the DL for UL transmission, mobile station'sretransmission may collide with other mobile stations.

Asynchronous HARQ has the benefit of being flexible in terms ofprioritization new transmission vs. retransmission. Therefore, itprovides better link adaptation/time diversity performance for very lowspeed cases. If the mobile station misses the control signaling of thefirst or any other sub-packet, there is still possibility to recover thepacket. However, it has the drawback of requiring more signalingoverhead compared to other schemes in order to indicate such parametersas HARQ channel identifiers (ACID), sub-packet identifiers (ID), HARQidentifier sequence number (AI-SN).

RAS-HARQ has the benefit of relatively small signaling overhead comparedto the asynchronous HARQ and flexible resource allocation andmultiplexing among users. However, it has the drawback of if the mobilestation misses the control signaling of first transmission and the basestation does not recognize that, it is not possible to recover thepacket.

There are several ways to perform retransmission in terms of theretransmission time interval, the resource location for theretransmission and the MCS used for the retransmission. Table 1 brieflysummarizes characteristics of retransmission for Synchronous HARQ,Asynchronous HARQ and RAS-HARQ.

TABLE 1 Characteristics of retransmission for synchronous HARQ,Asynchronous HARQ and Resource Adaptive Synchronous HARQ SynchronousAsynchronous HARQ HARQ RAS-HARQ Retransmission Fixed/ Variable,Fixed/predetermined time interval predetermined dynamically scheduledResource Same as first Variable, Variable, location sub-packetdynamically dynamically transmission assigned assigned MCS Same for Samefor Same for Chase, Chase, Chase, different for IR different fordifferent for IR IR

Error in control signaling impacts HARQ performance since controlinformation sent from the base station to the mobile station containscritical information for HARQ sub-packet combining. Two of the commontechniques of recombining sub-packets include Chase combining andIncremental Redundancy (IR). In the case of Chase combining, eachretransmission includes the same information. In the case of IR, eachretransmission contains different information than the previous one,such that every retransmission provides a receiver with additionalinformation.

IR provides both soft combining gain as well as coding gain. In someembodiments of the invention additional signaling overhead typicallyoccurring when IR is used is avoided by defining a sub-packet formatlookup table. For each MCS entry, the sub-packet format, i.e. modulationand effective coding rate derived from a mother code, is specified foreach retransmission trial. Some entries in the lookup table can beeffectively reduced to Chase combining when two consecutiveretransmission trials have the same sub-packet format.

In some embodiments of the invention, a 3-state acknowledgement channeland associated error recovery operation enables the base station andmobile station to recover from control signaling error and reduce packetloss.

While Asynchronous HARQ typically requires more signaling overhead thanother types of HARQ schemes, it allows more resource multiplexingflexibility at the base station. Asynchronous HARQ also allows the basestation to perform error recovery processes when needed. In someembodiments of the invention, RAS-HARQ may be used in combination withasynchronous HARQ.

HARQ acknowledgment and retransmission timing is at least in partdependent on processing delay at the base station and at the mobilestation. Time division duplex (TDD) downlink (DL) to uplink (UL) ratiosand the location of DL sub-frames and UL sub-frames being assigned fortransmission also affect the HARQ timing as the TDD DL to UL ratiosimpact when the DL and UL resources are available for retransmission andacknowledgement. In some embodiments of the invention, methods areprovided that enable self deducible HARQ timing at the mobile stationbased on the use of HARQ related parameters configured by the basestation.

In RAS-HARQ, only the resource location needs to be signalled forretransmissions. In some embodiments, there are multiple parallel HARQprocesses in progress for the same mobile station, where each HARQprocess corresponds to a first transmission and any retransmissions thatare necessitated of an encoder packet. Therefore, retransmissionsignaling according to RAS-HARQ involves uniquely identifying a HARQprocess as well as a resource assigned for the retransmission.

A first manner of signaling a retransmission involves transmittingsignalling information that includes an encoder packet ID to uniquelyidentify the encoder packet, and consequently the HARQ process, andresource assignment information for the retransmission. In someembodiments the signaling information is scrambled as a function of auser ID of the mobile station involved in the retransmission.

In some embodiments, with regard to a packet that is being subsequentlyretransmitted consistent with the first manner described above,signaling information for the initial transmission of that packetincludes a packet ID and resource assignment information for the initialtransmission. In some embodiments a user ID is also used for scrambling.In addition, other signalling information that is transmitted for theinitial transmission may include one or more of: the MCS; MIMO mode; andother characteristics that define the packet transmission.

A second manner of signaling a retransmission involves transmittingsignalling information that includes a resource ID of a previousretransmission and resource assignment information for theretransmission. The use of the resource ID of the previousretransmission can uniquely identify the HARQ process since each HARQprocess is assigned a different resource in the previous retransmission.In some embodiments the signaling information is scrambled as a functionof a user ID of the mobile station involved in the retransmission.

In some embodiments, with regard to a packet that is being subsequentlyretransmitted consistent with the second manner described above,signaling information for the initial transmission of that packetincludes a resource ID of the previous retransmission and resourceassignment information for the initial transmission. In some embodimentsa user ID is also used for scrambling. In addition, other signalinginformation that is transmitted for the initial transmission may includeone or more of: the MCS; MIMO mode; and other characteristics thatdefine the packet transmission.

With reference to FIG. 19, a method will now be described thatencompasses both the first and second manner described above. The methodinvolves, for a HARQ process, the HARQ process having a firsttransmission of an encoder packet and at least one retransmission, astep 19-1 of transmitting control information from a base station to amobile station for each respective transmission. The control informationincludes information to uniquely identify the HARQ process and anidentification of one of a time resource, a frequency resource and atime and frequency resource that is allocated for the transmission.

In some embodiments, the step of transmitting information to uniquelyidentify the HARQ process includes transmitting one of: an encoderpacket identifier (ID) to uniquely identify the encoder packet; and aresource identifier (ID) of a previous transmission.

Some examples of sub-frame control structures are presented in PCTpatent application PCT/2008/001986 filed Nov. 7, 2008 and U.S. patentapplication Ser. No. 12/202,741 filed Sep. 2, 2008, both of which areassigned to the assignee of the present application, and are herebyincorporated by reference in their entirety.

An example of RAS-HARQ will now be described with reference to FIG. 2.FIG. 2 illustrates at least part of a time resource, frequency resource,or time-frequency resource 200, used as a DL resource which ispartitioned into multiple time-frequency segments 210,220,230,240,250.Segment 210 is a UL Control Segment (UCS) used for assigning resourcesfor UL traffic. Each of segments 220,230,240,250 are DL Unicast Controland Traffic Segments used for assigning a particular DL unicast resourceand the resources used for the DL traffic for a respective mobilestation.

An expanded view of segment 210 includes a portion of segment 210 for aUL Combination Index 212 and multiple portions 214,216,218 of thesegment 212 for unicast control information for each UL resourceassignment. In some embodiments, the unicast control informationincludes retransmission control information that is used for signaling aretransmission in accordance with the first manner of signalingdescribed above. In some embodiments, the unicast control informationincludes retransmission control information that is used for signaling aretransmission in accordance with the second manner of signalingdescribed above.

An expanded view of segment 220 includes a portion of segment 220 for aDL Unicast Assignment Message 222 and a portion 224 of the segment 222for the unicast transmission. In some embodiments, the DL UnicastAssignment Message 222 includes retransmission control information thatis used for signaling a retransmission in accordance with the firstmanner of signaling described above. In some embodiments, the DL UnicastAssignment Message 222 includes retransmission control information thatis used for signaling a retransmission in accordance with the secondmanner of signaling described above.

DL Unicast Control and Traffic Segments 230, 240 and 250 include similarportions as segment 220 described above for different DL unicastassignments.

Referring to the general method described above in FIG. 19, in someembodiments, allocating a transmission resource for at least one unicastUplink (UL) transmission, transmitting control information includes astep of transmitting a UL control segment that is a portion of a DLtransmission resource, the UL control segment comprising a portion thatidentifies a location in the UL control segment for transmitting unicastcontrol information for each at least one unicast UL transmission and aportion that defines the control information for use in transmitting theunicast UL transmission.

Referring to the general method described above in FIG. 19, in someembodiments, allocating a transmission resource for at least one unicastDownlink (DL) transmission, transmitting control information comprises:for each at least one unicast DL transmission, transmitting a DL unicastcontrol and traffic segment comprising a portion of the DL unicastcontrol and traffic segment that defines the control information for usein transmitting the unicast DL transmission and a portion of the DLunicast control and traffic segment for transmitting data for therespective unicast DL transmission.

In some embodiments of the invention, a 3-state ACK channel (ACKCH) isused as part of the RAS-HARQ scheme. A first state used on the channelis an “ACK”, which indicates correct reception of a packet. A secondstate is a “NAK”, which is used to indicate failure in reception of apacket. A third state is a “NULL”, in which no signal is transmitted bya mobile station on the ACKCH. A NULL occurs when the mobile stationfails to detect the control signalling information corresponding to asub-packet transmission.

The following example describes an implementation of the 3-state ACKCHoperating from the perspective of a mobile station for DL.

The mobile station sends an ACK to the base station when the mobilestation succeeds in decoding a received packet.

The mobile station sends a NAK to the base station when the mobilestation fails to decode a received packet. After sending a NAK, themobile station waits for a retransmission from the base station. If themobile station does not receive any retransmission signaling within apredetermined time interval, the mobile station sends a NULL indicatingthat no retransmission signal was received.

There are different possibilities why the mobile station may not havereceived any retransmission signaling. A first possibility is that themobile station failed to detect the retransmission signalling from thebase station. This may be overcome by the base station detecting theNULL from the mobile station and the base station retransmitting theretransmission signaling. A second possibility is that the base stationdid not send a retransmission due to a NAK-to-ACK detection error at thebase station. This may occur when the base station incorrectly detectsan ACK when a NAK was sent by the mobile station. In this case, a packetfailure will likely occur.

In some implementations, the mobile station retains the HARQ buffercorresponding to an encoder packet until the expiry of a configurabletimeout period.

The following describes an implementation of the 3-state ACKCH operatingfrom the perspective of a base station for DL.

When the base station receives an ACK from a mobile station, the basestation does not perform retransmission to the mobile station. In someimplementations, as discussed above, this may result in noretransmission being sent when the base station incorrectly detects anACK, when a NAK was sent by the mobile station.

When the base station receives a NAK from the mobile station, the basestation retransmits a sub-packet to the mobile station at apredetermined time interval. A new resource assignment and encodedpacket ID, and possible a user ID is signaled as described above.

When the base station receives a NULL from a mobile station, the basestation will interpret that the mobile station has lost the signalingassociated with a sub-packet transmission.

If the transmission that was sent was a first sub-packet transmission,the base station will retransmit the first sub-packet in conjunctionwith the full signaling information, i.e. MCS, resource location, userID, MIMO information, packet ID etc. The base station can dynamicallyschedule the retransmission of this first sub-packet at any time.

If the transmission that was sent was a second or subsequent sub-packettransmission, the base station will retransmit at a predetermined timeinterval the corresponding sub-packet. In some embodiments, for thefirst manner of retransmitting signaling described above, the basestation sends the encoded packet ID, resource location information forthe current retransmission sub-packet and user ID. In some embodiments,for the second manner of retransmitting signaling described above, thebase station sends the original resource location of the firstsub-packet, resource location information of the current retransmissionsub-packet, and the user ID (for scrambling).

Referring to FIG. 20, a method will now be described for acknowledging aDL HARQ transmission. A first step 20-1 of the method involves receivingan encoder packet. A second step 20-2 involves, if the encoder packet issuccessfully decoded, transmitting an acknowledgement (ACK). A thirdstep 20-3 involves, if the encoder packet is not successfully decoded,transmitting a negative acknowledgement (NAK). A fourth step 20-4involves, if no retransmission is received within a predetermined timeperiod of transmitting the NAK, transmitting a NULL indicating that nocontrol information signalling pertaining to the retransmission has beenreceived.

The following describes an implementation of the 3-state ACKCH operatingfrom the perspective of a base station for UL.

When the base station fails to receive a packet, it schedules an ULretransmission of the sub-packet at the predetermined time interval. Inscheduling the UL retransmission the base station sends a new resourceassignment, a HARQ process identification or an encoded packetidentification and user ID to the mobile station.

When the base station succeeds in decoding a packet, no retransmissionis scheduled.

In some embodiments, the base station performs an error recoveryprocedure for the case when the mobile station fails to decode the firstsub-packet transmission signaling or the subsequent retransmissionsignalling. An example of an error recovery procedure is describedbelow.

For the case of first sub-packet transmission signaling, if the basestation fails to detect any UL transmission from the mobile station atthe assigned resource, the base station can resend the full signalinginformation, i.e. MCS, resource location, user ID (scrambled), MIMOinformation etc. In some embodiments the base station dynamicallyschedules the retransmission of this first sub-packet at any time.

For the case of retransmission signaling, i.e. second or subsequentsub-packet retransmissions, if the base station fails to detect any ULtransmission from the mobile station at the assigned resource, the basestation can send at the predetermined time interval a reduced amount ofsignaling information, in comparison to the signalling information sentfor the first transmission. For the first manner of retransmissionsignaling described above, the base station sends the encoded packet ID,resource assignment for the current retransmission sub-packet and userID. For the second manner of retransmission signaling described above,the base station sends the original resource assignment of the firstsub-packet, resource assignment of the next retransmission sub-packetand user ID.

Referring to FIG. 21, a method will now be described for acknowledging aDL HARQ transmission. A first step 21-1 of the method involves, if anacknowledgement (ACK) in response to a previously transmitted encoderpacket has been received, not retransmitting an encoder packet. A secondstep 21-2 of the method involves, if a negative acknowledgement (NAK) inresponse to a previously transmitted encoder packet has been received,retransmitting a sub-packet of the encoder packet. A third step 21-3 ofthe method involves, if a NULL is received indicating that no controlinformation signalling has been received by a sender of the NULLregarding a previously transmitted encoder packet, retransmitting atleast a sub-packet of the encoder packet.

In some embodiments, if the NULL is received in response to a previouslytransmitted sub-packet of an encoder packet that is a first sub-packettransmission, retransmitting the first sub-packet transmission, thefirst sub-packet transmission comprising control information signalingsent in a first sub-packet transmission.

In some embodiments, if the NULL is received in response to a previouslytransmitted sub-packet of an encoder packet that is a subsequentsub-packet transmission to a first sub-packet transmission,retransmitting the subsequent sub-packet transmission. The subsequentsub-packet transmission may include control information signaling suchas information to uniquely identify the HARQ process and anidentification of one of a time resource, a frequency resource and atime and frequency resource that is allocated for the subsequentsub-packet transmission.

Referring to FIG. 22, a method will now be described for rescheduling aUL HARQ transmission. A first step 22-1 of the method involves, if anencoder packet is not successfully decoded, scheduling an ULtransmission of a sub-packet at a predetermined time interval. A secondstep 22-2 involves transmitting control information pertaining to the ULtransmission according to the method described above with regard to FIG.19.

Referring to FIG. 23, a method will now be described for error recoveryfor a UL HARQ transmission. A first step 23-1 of the method involves, ifa NULL is received in response to a previously transmitted sub-packet ofan encoder packet that is a first sub-packet transmission, dynamicallyscheduling a retransmission of the first sub-packet transmission at anytime. A second step 23-2 involves retransmitting the first sub-packettransmission, the first sub-packet transmission comprising controlinformation signaling sent in a first sub-packet transmission.

A third step 23-3 involves, if a NULL is received in response to apreviously transmitted sub-packet of an encoder packet that is asubsequent sub-packet transmission to a first sub-packet transmission,scheduling a retransmission of the first sub-packet transmission at apredetermined time. A fourth step 23-4 involves, retransmitting thesubsequent sub-packet transmission. The subsequent sub-packettransmission includes control signaling information that includesinformation to uniquely identify the HARQ process and an identificationof one of a time resource, a frequency resource and a time and frequencyresource that is allocated for the subsequent sub-packet transmission.

The following describes an implementation of the 3-state ACKCH operatingfrom the perspective of a mobile station for UL.

When the mobile station receives the retransmission signaling from thebase station, the mobile station transmits the corresponding sub-packetin the assigned resource.

In some implementations, the mobile station retains the HARQ buffercorresponding to an encoded packet until the expiry of a configurabletimeout period.

Deducible DL HARQ Timing

The HARQ protocol timing should be flexible to adapt to different TDDDL/UL ratio and non-legacy (one example of which is IEEE802.16m)/legacypartitioning, without incurring unnecessary overhead. The minimum HARQACK delay and Retransmit (Retrx) delay and the number of HARQchannels/interlaces are defined in system/mobile station configurationsignaling which corresponds to particular partitioning of resources usedin legacy and non-legacy systems, and TDD DL/UL ratios. With theseparameters defined, the precise HARQ timing for ACK/NAK transmission andretransmission can be deduced as will be described below with referenceto FIGS. 3A to 3E. This concept can be applied to both TDD and frequencydivision duplexing (FDD).

In some embodiments, due to the asymmetrical DL/UL TDD (or FDD) ratio,the UL ACK of DL HARQ for multiple DL sub-frames may coincide in one ULsub-frame as shown in FIGS. 3A to 3E. The location of the ACKCH of amobile station within the UL sub-frame can be deduced from the HARQinterlace number, the assigned DL resource of the previous HARQsub-packet transmission, and the number of UL ACKCHs allocated per DLsub-frames as signaled in a superframe header. In some embodiments, asimilar approach is used for the case of DL acknowledgement of UL HARQas shown in FIGS. 4A to 4C.

Several examples will now be described to illustrate differentimplementations based on different TDD DL/UL ratios, ACK delay,retransmit delay and HARQ interlaces.

FIG. 3A illustrates two successive 5 ms radio frames 310,320 that eachinclude 8 sub-frames. Four sub-frames 311,312,313,314 are a portion ofthe first radio frame 310 used for DL transmission and retransmission.Sub-frames 311 and 312 are for use with legacy equipment and sub-frames313 and 314 are for use with equipment that supports IEEE802.16m. Foursub-frames 321,322,323,324 are a portion of a subsequent 5 ms radioframe 320 used for DL transmission and retransmission. Sub-frames 321and 322 are for use with legacy equipment and sub-frames 323 and 324 arefor use with equipment supports IEEE802.16m. Sub-frames 313 and 323 area first HARQ interlace “A” and sub-frames 314 and 324 are a second HARQinterlace “B”.

Four sub-frames 315,316,317,318 are a portion of the first 5 ms radioframe 310 used for UL acknowledgement (ACK). Sub-frame 315 is for usewith legacy equipment and sub-frames 316, 317 and 318 are for use withequipment that supports IEEE802.16m. Four sub-frames 325,326,327,328 area portion of the subsequent radio frame 320 used for UL ACK. Sub-frame325 is for use with legacy equipment and sub-frames 326, 327 and 328 arefor use with equipment that supports IEEE802.16m.

As there are two sub-frames allocated for IEEE802.16m DL transmissionand retransmission and three sub-frames allocated for UL ACKs, the TDDDL/UL ratio is 2:3.

The ACK delay, which is a delay between a transmission or retransmissionat the base station and an ACK being transmitted by the mobile station,is illustrated to be four sub-frames in the example of FIG. 3A. TheRetransmit delay, which is a delay between the ACK being transmitted atthe mobile station and the retransmission being transmitted by the basestation, is illustrated to be four sub-frames in the example of FIG. 3A.

FIG. 3A is an example having a particular set of parameters, i.e. TDDDL/UL ratio, ACK delay, Retransmit delay and HARQ interlace, 5 ms radioframe and 8 sub-frames per radio frame. It is to be understood that moregenerally these parameters are implementation specific and are notintended to limit the invention to a specific embodiment. Additionalexamples that follow below illustrate the use of different values forsome of the parameters. Furthermore, while only two radio frames areillustrated in FIG. 3A, the figure is exemplary of operation of thetiming scheme and as such the illustration of only two frames is notintend to limit the invention to what is described with reference toonly this particular example. In addition, the sub-frames are describedas supporting legacy and IEEE802.16m specifically, but it is to beunderstood that more generally the sub-frames may support legacy andnon-legacy transmissions.

FIG. 3B illustrates two successive 5 ms radio frames 330,340 and a DLtransmission portion of a third radio frame 350 in which in each frame,five sub-frames are used for DL transmission and retransmission andthree sub-frames are used for UL ACK. DL transmission sub-frames 331 and332 of the first frame 330 are for use with legacy equipment and DLtransmission sub-frames 333, 334 and 335 of the first frame 330 are foruse with equipment that supports IEEE802.16m. DL transmission sub-frames341 and 342 of the second frame 340 are for use with legacy equipmentand DL transmission sub-frames 343, 344 and 345 of the second frame 340are for use with equipment that supports IEEE802.16m. DL transmissionsub-frames 351 and 352 of the third frame 350 are for use with legacyequipment and DL transmission sub-frames 353, 354 and 355 of the thirdframe 350 are for use with equipment that is compliant with IEEE802.16m.

UL transmission sub-frame 336 of the first frame 330 is for use withlegacy equipment and UL transmission sub-frames 337 and 338 of the firstframe 330 are for use with equipment that supports IEEE802.16m. ULtransmission sub-frame 346 of the second frame 340 is for use withlegacy equipment and UL transmission sub-frames 347, includingsub-divided portions 347A and 347B, and 348 of the second frame 340 arefor use with equipment that is compliant with IEEE802.16m.

As there are three sub-frames allocated for IEEE802.16m DL transmissionand retransmission and two sub-frames allocated for UL ACKs, the TDDDL/UL ratio is 3:2.

In FIG. 3B there are 4 HARQ interlaces, sub-frames 333, 344 and 354 is afirst interlace “A”, sub-frames 334 and 345 are a second interlace “B”,sub-frames 335 and 352 are a third interlace “C” and sub-frames 343 and353 are a fourth interlace “D”.

The ACK delay and the Retransmit delay are each illustrated to be foursub-frames in the example of FIG. 3B.

In FIG. 3B, the sub-frame location within the radio frames for ACK andretransmission of a HARQ interlace change over time to accommodate theminimum ACK delay and Retransmit delay and retain the same ordering ofthe HARQ interlaces. For example, the ordering of the retransmissions inthe allocated sub-frames is maintained in the pattern “ABCD” as can beseen from A(sub-frame 333), B(sub-frame 334), C(sub-frame 335),D(sub-frame 343), A(sub-frame 344), B(sub-frame 345), C(sub-frame 352),D(sub-frame 353), A(sub-frame 355). The ordering of the ACKs in theallocated sub-frames is similarly maintained as “ABCD” as A(sub-frame337), B(sub-frame 338), C(sub-frame 347A), D(sub-frame 347B),A(sub-frame 348). As can be seen in FIG. 3B, the UL ACK in 347A and 347Bfor interlaces C and D, respectively, share a single sub-frame.

FIG. 3C illustrates an example which has a similar 8 sub-frame per frame5 ms radio frame, five sub-frame/three sub-frame per frame partition forDL transmissions and UL ACKs, four sub-frame ACK delay, 4 sub-frameRetransmit delay, and TDD DL/UL ratio of 3:2 as illustrated in FIG. 3B.In FIG. 3C the sub-frame location within a radio frame for ACK andretransmission of a HARQ interlace change over time to accommodate theminimum ACK delay and retransmission delay. However, the ordering of theHARQ interlaces can change over time. For example, the ordering of theretransmissions in the allocated sub-frames is “ABCABDCAB” as seen byA(sub-frame 363), B(sub-frame 364), C(sub-frame 365), A(sub-frame 373),B(sub-frame 374), D(sub-frame 375), C(sub-frame 383), A(sub-frame 384),B(sub-frame 385). The ordering of the ACKs in the allocated sub-framesfollows that of the transmitted pattern in the form A(sub-frame 367),B(sub-frame 368), C(sub-frame 377A), A(sub-frame 377B), B(sub-frame378). As can be seen in FIG. 3C, the UL ACK in 377A and 377B forinterlaces C and A, respectively, share a single sub-frame.

FIG. 3D illustrates an example which has a similar 8 sub-frame per frame5 ms radio frame, five sub-frame/three sub-frame per frame partition forDL transmissions and UL ACKs, four sub-frame ACK delay, 4 sub-frameRetransmit delay, and TDD DL/UL ratio of 3:2 as illustrated in FIG. 3B.

In FIG. 3D the sub-frame location within a radio frame for ACK andretransmission of a HARQ interlace is fixed. For example, the orderingof the retransmissions in the allocated sub-frames has the pattern“ABCABD” as shown by A(sub-frame 393), B(sub-frame 394), C(sub-frame395), A(sub-frame 403), B(sub-frame 404), D(sub-frame 405), A(sub-frame413), B(sub-frame 414), C(sub-frame 415). The ordering of the ACKs inthe allocated sub-frames is A(sub-frame 397), B(sub-frame 398),A(sub-frame 407), C(sub-frame 408A), B(sub-frame 408B), A(sub-frame417), D(sub-frame 418A), B(sub-frame 418B). As can be seen in FIG. 3D,the UL ACK in 408A and 408B for interlaces C and B, respectively, sharea single sub-frame and in 418A and 418B for interlaces D and B,respectively, share a single sub-frame.

FIG. 3E illustrates three successive 5 ms radio frames 500,510,520 inwhich in each frame, five sub-frames are used for DL transmission andretransmission and three sub-frames are used for UL ACK. All of the DLtransmission sub-frames in each of the frames are for use with equipmentthat supports IEEE802.16m. All of the UL transmission sub-frames in eachof the frames are for use with equipment that supports IEEE802.16m.

As there are five sub-frames allocated for IEEE802.16m DL transmissionand retransmission and three sub-frames allocated for UL ACKs, the TDDDL/UL ratio is 5:3.

In FIG. 3E there are 7 HARQ interlaces, sub-frames 501, 513 and 525 is afirst interlace “A”, sub-frames 502 and 514 are a second interlace “B”,sub-frames 503 and 515 are a third interlace “C”, sub-frames 504 and 521are a fourth interlace “D”, sub-frames 505 and 522 are a fifth interlace“E”, sub-frames 511 and 523 are a sixth interlace “F” and sub-frames 512and 524 are a seventh interlace “G”.

The ACK delay and the Retransmit delay are each illustrated to be foursub-frames in the example of FIG. 3B.

In FIG. 3E, the sub-frame location within a radio frame for ACK andretransmission of a HARQ interlace change over time to accommodate theminimum ACK delay and retransmission delay and retain the same orderingof the HARQ interlaces. For example, the ordering of the retransmissionsin the allocated sub-frames is “ABCDEFG” in the form A(sub-frame 501),B(sub-frame 502), C(sub-frame 503), D(sub-frame 504), E(sub-frame 505),F(sub-frame 511), G(sub-frame 512), A(sub-frame 513), B(sub-frame 514),C(sub-frame 515), D(sub-frame 521), E(sub-frame 522), F(sub-frame 523),G(sub-frame 524), A(sub-frame 525). The ordering of the ACKs in theallocated sub-frames is A(sub-frame 506A), B(sub-frame 506B),C(sub-frame 507), D(sub-frame 508), E(sub-frame 516A), F(sub-frame516B), G(sub-frame 516C), A(sub-frame 517), B(sub-frame 518),C(sub-frame 526A), D(sub-frame 526B), E(sub-frame 526C), F(sub-frame527), G(sub-frame 528). As can be seen in FIG. 3E, the UL ACK in 506Aand 506B for interlaces A and B, respectively, share a single sub-frame,in 516A, 516B and 516C for interlaces E, F and G, respectively, share asingle sub-frame and in 526A, 526B and 526C for interlaces C, D and E,respectively, share a single sub-frame.

Deducible UL HARQ Timing

The minimum HARQ ACK and Retransmit delay and the number of HARQchannels are defined in system broadcast signaling which corresponds toparticular partitioning of legacy and IEEE802.16m, and TDD DL/UL ratios.With these parameters defined, the precise HARQ timing can be deduced.This concept can be applied to both TDD and FDD.

FIG. 4A illustrates two successive 5 ms radio frames 420,430 that eachinclude 8 sub-frames. Three sub-frames 421,422,423 are a portion of thefirst radio frame 420 used for UL transmission and retransmission.Sub-frame 421 is for use with legacy equipment and sub-frames 422 and423 are for use with equipment that supports IEEE802.16m. Threesub-frames 431,432,433 are a portion of a subsequent 5 ms radio frame430 used for UL transmission and retransmission. Sub-frame 431 is foruse with legacy equipment and sub-frames 432 and 433 are for use withequipment that supports IEEE802.16m. Sub-frames 422 and 432 are a firstHARQ interlace “A” and sub-frames 423 and 433 are a second HARQinterlace “B”.

Five sub-frames 424,425,426,427,428 are a portion of the first 5 msradio frame 420 used for DL acknowledgement (ACK). Sub-frames 424 and425 are for use with legacy equipment and sub-frames 426, 427 and 428are for use with equipment that supports IEEE802.16m. Five sub-frames434,435,436,437,438 are a portion of the subsequent radio frame 430 usedfor DL ACK. Sub-frames 434,435 are for use with legacy equipment andsub-frames 436, 437 and 438 are for use with equipment that supportsIEEE802.16m.

As there are two sub-frames allocated for IEEE802.16m UL transmissionand retransmission and three sub-frames allocated for DL ACKs, the TDDDL/UL ratio is 3:2.

The ACK delay is illustrated to be four sub-frames and the Retransmitdelay is also illustrated to be four sub-frames in the example of FIG.4A.

FIG. 4B illustrates two successive 5 ms radio frames 440,450 and a DLtransmission portion of a third radio frame 460 in which in each frame,four sub-frames are used for DL transmission and retransmission and foursub-frames are used for UL ACK. UL transmission sub-frame 441 of thefirst frame 440 is for use with legacy equipment and UL transmissionsub-frames 442, 443 and 444 of the first frame 440 are for use withequipment that supports IEEE802.16m. UL transmission sub-frame 451 ofthe second frame 450 is for use with legacy equipment and ULtransmission sub-frames 452, 453 and 454 of the second frame 450 are foruse with equipment that supports IEEE802.16m. UL transmission sub-frame461 of the third frame 460 is for use with legacy equipment and DLtransmission sub-frames 462, 463 and 464 of the third frame 460 are foruse with equipment that supports IEEE802.16m.

DL ACK sub-frames 445 and 446 of the first frame 440 are for use withlegacy equipment and DL ACK sub-frames 447, including sub-dividedportions 447A and 447B, and 448 of the first frame 440 are for use withequipment that supports IEEE802.16m. DL ACK sub-frames 455 and 456 ofthe second frame 450 are for use with legacy equipment and ULtransmission sub-frames 457, including sub-divided portions 457A and457B, and 458 of the second frame 450 are for use with equipment thatsupports IEEE802.16m.

As there are three sub-frames allocated for IEEE802.16m UL transmissionand retransmission and two sub-frames allocated for DL ACKs, the TDDDL/UL ratio is 2:3.

In FIG. 4B there are 4 HARQ interlaces, sub-frames 442, 453 and 464 is afirst interlace “A”, sub-frames 443 and 454 are a second interlace “B”,sub-frames 444 and 462 are a third interlace “C” and sub-frames 452 and463 are a fourth interlace “D”.

The ACK delay and the Retransmit delay are each illustrated to be foursub-frames in the example of FIG. 4B.

In FIG. 4B, the sub-frame location within a radio frame for ACK andretransmission of a HARQ interlace change over time to accommodate theminimum ACK delay and Retransmit delay and retain the same ordering ofthe HARQ interlaces. For example, the ordering of the retransmissions inthe allocated sub-frames is “ABCD” as seen by A(sub-frame 442),B(sub-frame 443), C(sub-frame 444), D(sub-frame 452), A(sub-frame 453),B(sub-frame 454), C(sub-frame 462), D(sub-frame 463), A(sub-frame 464).The ordering of the ACKs in the allocated sub-frames is A(sub-frame447A), B(sub-frame 447B), C(sub-frame 448), D(sub-frame 457A),A(sub-frame 457B), B(sub-frame 458). As can be seen in FIG. 4B, the DLACK in 447A and 447B for interlaces A and B, respectively, share asingle sub-frame and in 457A and 457B for interlaces D and A,respectively, share a single sub-frame.

FIG. 4C illustrates an example which has a similar 8 sub-frame per frame5 ms radio frame, four sub-frame/four sub-frame per frame partition forUL transmissions and DL ACKs, four sub-frame ACK delay, 4 sub-frameRetransmit delay, and TDD DL/UL ratio of 2:3 as illustrated in FIG. 4B.In FIG. 4C the sub-frame location within a radio frame for ACK andretransmission of a HARQ interlace change is fixed. For example, theordering of the retransmissions in the allocated sub-frames is“ABCDBCABC” as shown by A(sub-frame 472), B(sub-frame 473), C(sub-frame474), D(sub-frame 482), B(sub-frame 483), C(sub-frame 484), A(sub-frame492), B(sub-frame 493), B(sub-frame 494). The ordering of the ACKs inthe allocated sub-frames is A(sub-frame 477A), B(sub-frame 477B),C(sub-frame 478) D(sub-frame 487A), B(sub-frame 487B), C(sub-frame 488),A(sub-frame 497A), B(sub-frame 497B), B(sub-frame 498). As can be seenin FIG. 4C, the DL ACK in 477A and 477B for interlaces A and B,respectively, share a single sub-frame and in 487A and 487B forinterlaces D and B, respectively, share a single sub-frame and in 497Aand 497B for interlaces A and B, respectively, share a single sub-frame.

Referring to FIG. 24, a method will now be described for determining thetiming for receiving an ACK/NAK at a base station. A first step 24-1 ofthe method involves, in a system having a known HARQ acknowledgement(ACK) delay, retransmit delay and number of HARQ interlaces, which areeach defined in configuration signalling sent to a mobile station andwhich are a function of at least one of a time division duplexingdownlink/uplink (TDD DL/UL) ratio and a frequency division duplexingdownlink/uplink (FDD DL/UL) ratio, at the base station, determining thetiming for receiving an ACK/NAK from a mobile station based onconfiguration signalling in response to a previously sent transmissionof an encoder packet by the base station.

In some embodiments, a further step of the method involves sending theconfiguration signalling.

Referring to FIG. 25, a method will now be described for determining thetiming for receiving one of a transmission and a retransmission of asub-packet of an encoder packet at a mobile station. A first step 25-1of the method involves, in a system having a known HARQ acknowledgement(ACK) delay, retransmit delay and number of HARQ interlaces, which areeach defined in configuration signalling sent to a mobile station andwhich are a function of at least one of a time division duplexingdownlink/uplink (TDD DL/UL) ratio and a frequency division duplexingdownlink/uplink (FDD DL/UL) ratio, at the mobile station, determiningthe timing for receiving one of a transmission and a retransmission of asub-packet of an encoder packet at a mobile station based on theconfiguration signalling in response to a previously sent NAK by themobile station.

In some embodiments, a further step of the method involves receiving theconfiguration signalling.

Packet transmissions can be persistent assignments, or non-persistentassignments signalled within specific resource partitions. A persistentresource assignment is an assignment of a predefined, usuallyreoccurring, resource to a user, such that assignment to that user doesnot require further signaling for each reoccurrence. Persistentassignments are indicated to other users by a resource availabilitybitmap (RAB). Examples of implementing an RAB can be found in PCT patentapplication PCT/2008/001980 filed Nov. 5, 2008, which is commonlyassigned to the assignee of the present application and which isincorporated herein by reference in its entirety.

Group assignment of resources using a bitmap is used for non-persistentpacket assignments. Each group is assigned a separate resourcepartition.

In some embodiments division and identification of available resourcesis indicated by a multicast control segment (MCCS).

In some embodiments, partition of zones is signalled by combinationindex (CI) which signals the resource partitions within the persistentand non-persistent zones. Examples of a RAB can be found in commonlyassigned PCT/2008/001980.

In some embodiments, a look-up table is created with possible resourcepartitions, for a given total number of resources. For example, possiblepartitioning of 12 resources can be given by {1,2,4,6}.

Each entry of the look-up table is specified by the CI index. The CI canbe transmitted in bit-form, proper encoded, at the beginning of frame.If a persistent sub-zone is specified, the RAB may be sent. In someembodiments, the CI is concatenated and encoded with the RAB. The RAB isa bitmap that indicates which resources are available, and which areoccupied with a persistent HARQ transmission. The RAB contains one bitfor every resource (or resource block), and the value of the bitindicates whether the resource is in use or available.

Persistent resources that are unused due to packet arrival jitter,silence state, or early termination of HARQ transmissions are shown asavailable.

In some embodiments, for reliability, a CRC is appended to theconcatenated CI and RAB. The resource partitions indicated by the CIdivide the set of resources remaining after resources indicated asoccupied by the RAB are removed from the resource list. In someembodiments, the size of the persistent zone is transmitted in asecondary broadcast channel.

Referring to FIG. 5, an example of a resource availability bitmap willnow be described. FIG. 5 illustrates at least part of a frame 900,having a combination index 910, an RAB 915, a persistent zone 920 thathas at least some resources that are persistently assigned, and anon-persistent zone 930 that has no persistently assigned resources. Thecombination index 910 and the RAB 915 may together be referred to as amulticast control segment (MCCS). In the persistent zone there are threepartitions 921,924,927. Two of the partitions 921,924 are groupassignments and have signaling bitmaps 922,925, respectively. The thirdassignment 927 is an Uplink Control segment (ULCS) for defining unicastassignments. In some embodiments, the UCTS may be implemented in amanner similar to that described above with reference to FIG. 2.

In the Non-persistent Zone 930, one of the partitions 940 is a Groupcontrol and traffic segment (GCTS) which is used for defining groupassignments. Two other partitions 930 and 950 are Unicast control andtraffic segments (UCTS) used for defining unicast assignment. In someembodiments, the UCTS may be implemented in a manner similar to thatdescribed above for the DL UCTS with reference to FIG. 2.

With reference to group assignment 924, group assignment 924 has asignaling bitmap 925 that includes an assignment bitmap 940, a pairingor sets combination index bitmap 941 and a resource permutation indexbitmap 942. The assignment bitmap 940 has 6 bits, one bit for possibleassignment to each user. The pairing or sets combination index bitmap941 has 4 bits. The resource permutation bitmap 942 has 2 bits. Groupassignment 921 has a signaling bitmap as well.

In group assignment 924 also indicated is a persistently assignedresource 926 (gray shaded portion of group assignment 924) that is inuse and as such is not available for assignment to other users. Similarpersistent assignments are shown in group assignments 921 and 927.

In some embodiments, superposition can be used to transmit multiplepackets on the same resource by making use of different users'geometries, and an altered packet structure for to enable interferencecancellation of some packets while maintaining security.

In some embodiments, superposition of multiple assignments can beachieved by assigning them to the same resources, or set of resources.In some embodiments, this process can be used to superpositionpersistent and non-persistent assignment.

Multiplexing of persistent assignments can be achieved by indicating a“busy” resource, as available in the RAB. By indicating a persistentused resource as available in the RAB, other indicated assignments willuse the resource as well (groups or otherwise). Hence the persistenttransmission and other transmissions will be sent simultaneously on thesame resource. If all persistent assignments are to be indicated asavailable, the RAB does not need to be sent.

In some embodiments, superposition can also be used to multiplex userson the downlink by allowing a persistent user and other signalleduser(s) to be allocated to the same resource. This is useful formulti-user MIMO applications. Superposition of the persistent assignmentand signalled assignment can be achieved this way.

A decision to indicate a persistent assignment resource that is in useas “busy” or “available” in the RAB can be made at the base stationdynamically for each assignment, in each time frame.

The decision may be based on at least one of: geometries of mobiles forwhich the different packets are intended and reliability of thedifferent packets. Users that have high geometry are users that havegood long-term channel conditions for communicating with their servingbase station. Therefore, it is desirable in some situations to providebitmaps for users with generally good channel conditions.

A mobile station is configured to check for presence of superpositionedpersistent assignment by determining that its transmission occurs in thepersistent sub-zone. In some embodiments the mobile station isconfigured to check for presence of superpositioned persistentassignment by detecting an indication of a “number of layers” field,which can be appended to the CI (within MCCS field). In someembodiments, the field may correspond to the number of layers, eithersuperposition or MIMO, for each partition. In some embodiments, themobile station is configured to check for presence of superpositionedpersistent assignment based on received power threshold detection. Insome embodiments, the mobile station is configured to always check forpresence of superpositioned persistent assignment.

In some embodiments the packet intended for the lower geometry mobilestation (e.g. persistent assignment) can be encoded in a manner thatallows it to be decoded. In some embodiments, the decoding is verifiedwith the use of a CRC, which enables the transmission to be used forinterference cancellation (IC). However, users that decode thetransmission will not be able to have access to the usable data as itwill remain scrambled by the intended user's identification (ID)sequence.

In some systems, a persistent assignment can be used. Persistentassignment is defined as an assignment on a predefined resource for oneor more HARQ transmissions. It is possible to assign other user(s) tothe same resource. Unicast or group signaling are two examples of suchsignaling methods to assign these resources.

The base station may utilize the same resource for transmitting one ormore persistent assignments, and one or more signaled assignments inorder to improve capacity. The persistent packet transmission is alteredin a manner to allow the mobile station receiving a non-persistenttransmission to receive and decode it for the purpose of interferencecancellation, without the ability to descramble it. A mobile stationreceiving a persistent transmission decodes the altered packet in aregular fashion, adding extra steps to undo the alteration to allow itto be decoded for the purpose of interference cancellation of thepacket.

In general, when two or more packets are superpositioned on the DL andare intended for different users, the packet transmission with a higherreliability (packet A) is altered in a manner to allow the mobilestation intended to receive a different transmission (with lowerreliability, (packet B)), to receive the higher reliability transmission(packet A) and decode it for the purpose of interference cancellation,without the ability to descramble it. A mobile station intended toreceive a packet that has been altered to allow a different user(s) todecode it for the purpose of interference cancellation, decodes thealtered packet in a regular fashion, but includes extra steps to undothe alteration the packet. A mobile station intended to receive thealtered packet (packet A) transmission that has been superpositionedwith another packet decodes the altered packet.

As the packet that is sent at higher reliability may be readily decodedat a different mobile station after only one transmission, the mobilecan make use of the decoded higher reliability packet for interferencecancellation of its own transmission in each frame. One transmission canbe sent with “higher reliability” by any one of, but not limited to:using a higher power level; using a more robust coding scheme; and usinga higher processing gain (i.e. spreading). This process may be used forboth Chase combining case and incremental redundancy (IR) HARQtransmission case.

Process for Superpositioned Packet to be Used in InterferenceCancellation

The packet intended for the lower geometry mobile (e.g. persistentassignment) can be encoded in a manner that allows it to be decoded byothers users, and verify decoding with a CRC, enable use of thetransmission for efficient interference cancellation (IC). However,these user with not be able to have access to the usable data as then itwill remain scrambled by the intended users identification sequence.

This process involves using two cyclic redundancy checks (CRC's); afirst CRC is applied before scrambling by the intended useridentification sequence and a second CRC is applied after. Other mobilestations will be able to use the second CRC for confirming correctdecoding of the transmission, while the first CRC confirms the intendeduser of the packet after correct descrambling.

In order to enable superposition and detection involving interferencecancellation of one or more layers of packets for applications such astransmission of two (or N, where N equals the numbers of users)different packets, to two (or N) different users. The packet that issent at higher reliability can be further appended with a CRC andscrambled with an identifying sequence, in addition to normal encodingand scrambling procedures.

Referring to FIG. 6A, an example of how a packet 610 with an appendedCRC ‘A’ 612 is scrambled and encoded in a conventional manner will nowbe described. The packet 610 includes N data bits. The CRC ‘A’ 612 isappended to the end of packet 610. The combined data and CRC arescrambled using an identification sequence. In some implementations theidentification sequence may be one of, but not limited to, a sector IDand a userID or a MAC ID, to create a scrambled packet 620. Thescrambled packet is then encoded, to created an encode packet 630. Insome implementations the encoding may be one of, but not limited to,turbo encoding, convolutional encoding, LDPC encoding.

Referring to FIG. 6B, an example of how a packet 640 with an appendedCRC ‘A’ 642 is scrambled and encoded and then the encoded packet 660appended with another CRC ‘B’ 662 and scrambled again according to anembodiment of the invention will now be described. Such a method can beused in interference cancellation for superpositioned packets.

The first several steps are similar to the steps described above withregard to FIG. 6A and result in an encoded, scrambled packet 660. A CRC‘B’ 662 is appended to the end of the encoded, scrambled packet 660. Theencoded packet 660 and CRC ‘B’ 662 are scrambled using an additionalidentification sequence known to multiple users to create a scrambledpacket 670, thus allowing any of the multiple users to descramble thescrambled packet. In some implementations the identification sequencemay be a sector ID. The scrambled packet 670 is then encoded, to createan encoded packet 680. In some implementations the encoding may be oneof, but not limited to, turbo encoding, convolutional encoding, LDPCencoding.

The second scrambling step is optional and may not be used in alimplementations.

In some cases for either process, the scrambling with identificationsequence can be performed on the data only, CRC only, or both Data+CRC.

Other scrambling, interleaving, modulation blocks may be added to thischain. Only essential steps significant to this description areincluded.

Process for Detection and Reception of Packets at Two Mobiles

Referring to FIG. 7, an example of how superpositioned packets may betransmitted and decoded using interference cancellation according to thedouble scrambling and double encoding described above, will now bedescribed.

Mobile Station A 720, at a lower relative geometry, is intended toreceive Packet A 712 that has been altered according to doublescramble/double encoding described above. The resource for transmittingthe packet may be persistently assigned.

Mobile Station B 730, at a higher relative geometry, is intended toreceive Packet B 714 that has been encoded according to singlescramble/single encoding described above. Both packets are sent on theysame resource. If the transmission for Packet A 712 is persistentlyassigned, the resource is indicated as “available” on the RAB. It ispossible that multiple packets belonging to one on more users are senton resources that overlap for some transmissions.

Process at Mobile A

An attempt to decode and descramble the “outer layer” of encoding andscrambling, if the outer layer of scrambling is used, is made for PacketA 712, using CRC ‘B’ for verification of correct decoding. If Packet A712 is decoded successfully, the packet is descrambled with anidentification sequence using CRC ‘A’ for verification of correctdecoding/descrambling. If not decoded successfully, a re-transmissionprocess is followed as specified by HARQ, if desired. In someembodiments, this may include RAS-HARQ retransmission using the controlinformation signaling techniques described above.

For example, in HARQ the unsuccessful transmission may be retained atthe mobile to be combined in some way (incremental redundancy or chasecombining) with additional retransmissions.

Process at Mobile B

An attempt to decode and descramble (if used) packet A, is made usingCRC ‘B’ for verification of correct decoding.

If decoded successfully, interference cancellation can be used toessentially remove Packet A 712 from the combined transmission of PacketA 712 and Packet B 714, which is intended for Mobile B 730, since thetwo packets are transmitted in the same resource. If Packet B 714 is notdecoded successfully, HARQ schemes can be used to try to recover thepacket.

If other packets are superpositioned, either partially or completelywith Packet B, an attempt can be made to detect and cancel these packetas well using similar processes of successive interference cancellation.From the resulting signal, an attempt can be made to decode Packet B. Ifdesired, a HARQ re-transmission process can be used in recovering anddetecting the packet.

For example, in HARQ the unsuccessful transmission may be retained atthe mobile to be combined in some way (incremental redundancy or chasecombining) with additional retransmissions. Successfully decoded packetsintended for other users can be used for additional channel estimationreliability. Power level may need to be detected blindly, if not known.

Benefits of the above process include:

1) enabling superposition, and thereby reducing resources used fortransmission (capacity enhancement);

2) making use of targeting different geometries so that a transmissionsare sent with different reliabilities. In some embodiments, atransmission arrives at a different mobile, and can be reliably receivedto enable interference cancellation without re-transmissions. In someembodiments, transmission intended for mobile with lower geometry is notsignificantly affected by presence of superpositioned packet;

3) allowing a mobile station to decode and use a packet intended for adifferent mobile for the purpose of interference cancellation, withoutallowing the mobile to de-scramble the actual usable data;

4) allowing persistent resources to be indicated as “available”, whichallows the RAB to be shortened or omitted as default without RAB forresources is “available”;

5) the additional cost is only an additional CRC appended totransmissions.

In some embodiments the process is especially useful for VoIPapplications as packet sizes/coding rates/modulation schemes are limitedto a finite number of hypothesis. In some applications, the VoIP packetto used for interference cancellation may be a fixed parameter (or verylimited set). For example, one modulation and coding scheme for eachpacket size, with fixed resource allocation size.

DL Control Channel Structure

In some embodiments, subzones can be created within a frame structure toenable DL channel control. A frame is a physical construct fortransmission that once it is set is not changed, while a subzone is aportion a frame that is configurable as a scheduling construct, whosesize and shape may change within the frame for a given situation. Forexample, in an OFDM application, subzones may consist of multiples of 2OFDM symbols over a block of sub carriers. In some embodiments, theblock of sub-carriers is the entire set of the sub-carriers of anavailable band.

In some embodiments, a basic channel unit (BCU) allocation block (BAB)may consist of one or more BCUs. A BCU is a two dimensionaltime-frequency transmission resource, i.e. a given number of symbolsover a given number of sub-carriers. The sub-carriers may be physicalsub-carries or logical sub-carriers that are permuted based on aparticular mapping of physical sub-carries to logical sub-carries. Insome embodiments, within a subzone, a BAB has a same number oftime-frequency resource blocks per OFDM symbol. In some embodiments,this may be true when averaged over one or more frames. While OFDMsymbols are referred to specifically, it is to be understood that OFDMis considered for illustrative purposes, and other transmission formatsare contemplated.

In some embodiments, different subzones may have different BABconfigurations. For example, a first subzone has 4 OFDM symbols in whicheach BAB has 2 BCUs. In another example, a second subzone has 4 OFDMsymbols, in which some BABs have 4 BCUs and other BABs have 8 BCUs. Inyet another example, a third subzone has 6 OFDM symbols, in which eachBAB has 12 BCUs.

In some embodiments, an extended frame can be supported by defining aseparate zone. The BCUs in the separate zone of the extended frame usethe same channelization as in the non-extended frame zone. No additionalcomplexity is required.

In some embodiments, in the separate zone of the extended frame, thecontrol channel, be it an MCCS or a unicast control channel, occursevery k frames. Each assignment in the separate zone of the extendedframe is for k frames.

The unicast control information is contained within an associatedpartition in the first sub-frame. In this design, transmissions usingextended sub-frames can co-exist with transmissions using non-extendedsub-frames. This way only the mobiles that use the extended zone areaffected by the increased latency.

A separate zone in the extended frame can be defined for ULtransmissions as well for DL transmissions.

In some embodiments, an access grant message contains a user ID of amobile station that initiated a request for access. An access grantmessage is contained in a UL control segment and it is scrambled by thesequence that the mobile station used in the UL random access channel.

In some embodiments, the UL control segment contains the followingfields: an MCCS, a unicast assignment message, a group assignmentmessage and a UL access grant message. The MCCS contains a combinationindex and/or permutation index and a RAB if persistent resources havebeen allocated. Examples pertaining to implementation of the combinationindex, permutation index and RAB can be found in commonly assignedPCT/2008/001980. The unicast assignment message may include multipleunicast assignment messages, one for each assignment. The groupassignment message may include multiple group assignment messages, onefor each assignment.

Persistent resources are allocated using a persistent assignmentmessage. There are separate persistent assignment messages for both DLand UL assignments. In some embodiments, each message contains aresource ID (BCU) and a number of resources assigned. In someembodiments each message contains a bitmap indicating the assignedresources. In the bitmap approach, the length of the bitmap is thelength of the persistent zone. In some embodiments, the length of thepersistent zone is signalled in a super-frame control.

In some implementations, a UL persistent assignment message is containedin the UL control segment. In some implementations, the UL persistentassignment message is contained in a separate partition.

In some implementations, DL/UL persistent assignment messages arescrambled by the user ID of the intended user.

In a multi-user MIMO (MU-MIMO) case, in which multiple users areassigned to a same partition of a transmission resource, separateunicast messages are provided for each user assigned to the samepartition.

In some embodiments, the unicast control segment contains a MU-MIMOheader, which is a multicast message that is targeted to the lowestgeometry user in the assignment. The MU-MIMO header contains informationidentifying a message type, which indicates a number of layers that aremultiplexed on to the same resource and a pre-coding matrix index (PMI)that is used for the transmission in the case of codebook basedpre-coding feedback. The PMI is a matrix with a number of columns equalto the number of layers that are multiplexed on a resource. Each columnconsists of a pre-coding vector for the corresponding layer.

In some embodiments, the MU-MIMO header is CRC protected. This is thenfollowed by individual unicast messages for each assignment. Theindividual unicast messages contain the MCS of the assignment. In someimplementations each unicast message is scrambled by the user ID of theintended user. In some implementations the unicast messages are CRCprotected.

In some embodiments, the DL ACK channel is used to acknowledge UL datatransmission. A fixed number of diversity resources are allocated to agroup of control channels that includes, but is not limited to: DL ACK;UL power control channel; and the MCCS.

In some implementations, the number of resources for the DL ACK channelsand the location of the resources are signalled in a super-framecontrol. In some implementations, each DL ACK channel consists of Ntones that are spread over the entire band. In some implementations,each DL ACK channel is power controlled to the intended user. In someimplementations, for the DL power control channel, one channel isassigned to each user for the purpose of power control.

Multi-Carrier Configuration for OFDM System

According to another aspect of the invention there are provided methodsfor adjacent multi-carrier configuration of OFDM system to ensuresub-carriers alignment between adjacent carriers.

In a current WiMAX/802.16e schemes, the frequency raster of 250 kHz isnot divisible by the WiMAX/802.16e sub-carrier spacing of 10.94 kHz. Ina situation where the spacing of center frequencies of adjacent carriersare an integer multiple of the raster size of 250 kHz, the OFDMsub-carriers between two adjacent carriers are not aligned. Referring toFIG. 8, an example is illustrated in which a first carrier is shownhaving a first set of sub-carriers and a second carrier is shown havinga second set of sub-carriers. The spacing of the center frequencies ofthe first carrier and the second carrier is N×250 kHz, which is notdivisible by 10.94 kHz. This situation of non-aligned sub-carriers willcause inter-carrier interference.

A proposed solution to this problem is changing the sub-carrier spacingto 12.5 kHz which is divisible by raster size of 250 kHz. However, thissolution introduces a new sub-carrier spacing that is not backwardcompatible with existing WiMAX schemes.

To support backward compatibility, three sets of OFDM sub-carrierspacing have been adopted in IEEE 802.16m-08/003r1. These spacingsinclude 7.81 kHz, 9.77 kHz and 10.49 kHz. However, details regardingadjacent carrier configuration such as carrier spacing, sub-carrieralignment and guard tones have not been described.

For the cases of sub-carrier spacing of 7.81 kHz and 9.77 kHz, thecorresponding system bandwidth is divisible by the proposed sub-carrierspacings. Therefore, in a multicarrier deployment, the centerfrequencies of adjacent carriers are spaced by integer number ofsub-carriers.

In a case in which a wireless device that is compatible with IEEE802.16mis used for communication, there is a zone of a resource allocated forIEEE802.16m transmissions. No guard tones are required on sub-frameswithin the IEEE802.16m zone between adjacent carriers beyond the carrierbandwidth.

However, to support backward compatibility, sub-frames within a zoneallocated for legacy supported carriers contain guard tones betweenadjacent carriers. In some implementations, guard tones between adjacentcarriers are consistent with those guard tone arrangements defined inlegacy system permutation formats.

With reference to FIG. 9, an example of two adjacent carriers eachhaving both legacy and IEEE802.16m DL and UL sub-frame components willnow be discussed.

A first carrier 510, having multiple sub-carriers that are notindividually shown, but rather which are shown as a block of frequenciesin the vertical direction is illustrated over two successive 5 ms radioframes 530,550. A DL portion of each radio frame includes foursub-frames, two of which are legacy sub-frames 533 and two of which areIEEE802.16m sub-frames 534. A UL portion of each radio frame includesfour sub-frames, one of which is a legacy sub-frames 543 and three ofwhich are IEEE802.16m sub-frames 544.

A second carrier 520, having multiple sub-carriers in a block offrequencies in the vertical direction is illustrated over two successive5 ms radio frames. A DL portion of each radio frame includes foursub-frames, one of which is a legacy sub-frames 537 and three of whichare IEEE802.16m sub-frames 538. A UL portion of each radio frameincludes four sub-frames, two of which are legacy sub-frames 5473 andtwo of which are IEEE802.16m sub-frames 548.

In the first carrier 510, some sub-carriers of the legacy DL sub-frames533 are allocated as guard tones 535 between the sub-carriers of thefirst carrier 510 and the sub-carriers of the second carrier 520. In thesecond carrier 520, some sub-carriers of the legacy DL sub-frames 537are allocated as guard tones 536 between the sub-carriers of the secondcarrier 520 and the sub-carriers of the first carrier 510. However, noguard tones are needed between the sub-carriers of the first carrier 510and the sub-carriers of the second carrier 520, or vice versa, if thesub-frames are IEEE802.16m sub-frames.

In the first carrier 510, some sub-carriers of the legacy UL sub-frames543 are allocated as guard tones 545 between the sub-carriers of thefirst carrier 510 and the sub-carriers of the second carrier 520. In thesecond carrier 520, some sub-carriers of the legacy UL sub-frames 547are allocated as guard tones 546 between the sub-carriers of the secondcarrier 520 and the sub-carriers of the first carrier 510. However, noguard tones are needed between the sub-carriers of the first carrier 510and the sub-carriers of the second carrier 520, or vice versa, if thesub-frames are IEEE802.16m sub-frames.

FIG. 9 is a particular example for a given size radio frame, number ofDL and UL sub-frames and arrangement of legacy and IEEE802.16m supportedcarriers. These parameters are implementation specific and therefore theparticular example of FIG. 9 is not intended to limit the invention.Furthermore, while IEEE802.16m supported carriers are specificallyreferred above, more generally, the invention can be applied to othersupported carriers that are non-legacy supported carriers.

For the case of sub-carrier spacing of 10.94 kHz, system bandwidths of5/10/20 MHz are not divisible by the sub-carrier spacing. However,N×1.75 MHz, e.g. 5.25 MHz, 10.5 MHz, 21 MHz are divisible by thesub-carrier spacing. In a situation in which two adjacent carriers arelegacy support carriers, the center frequencies of the adjacent carriersare spaced apart by the carrier bandwidths in order to ensure backwardcompatibility. Guard tones are used between the adjacent carriers.

If a non-legacy support carrier is adjacent to a legacy support carrier,the center frequency of the non-legacy carrier can be offset such thatthe center frequencies of the two adjacent carriers can be spaced by5.25/10.5/21 MHz respectively for carrier bandwidth of 5/10/20 MHzrespectively. Therefore, the center frequency spacing of adjacentcarriers can be set to multiples of 5.25 MHz to avoid the sub-carriermisalignment issue. For example, two adjacent 5 MHz carriers are spacedby 5.25 MHz. Two adjacent 10 MHz carriers are spacing by 10.5 MHz. Anillustration for carrier bandwidth of 5 MHz is shown in FIG. 10. For thenon-legacy carrier, as shown in Figure (next slide), uneven number ofguard sub-carriers are used on both sides of a carrier.

On a sub-frame within the non-legacy carrier supported zone, no guardtones are required between adjacent carriers beyond the carrierbandwidth. On a sub-frame within the legacy carrier supported zone,guard tones are still used between adjacent carriers on sub-frameswithin the legacy zone.

FIG. 11 illustrates an example of two adjacent carriers one havinglegacy support carriers and one having non-legacy supported carrier intwo consecutive 5 ms radio frames 1130,1150.

A first carrier 1110 that includes legacy support, having multiplesub-carriers that are not individually shown, but rather which are shownas a block of frequencies in the vertical direction is illustrated overtwo successive 5 ms radio frames. A DL portion of each radio frameincludes four sub-frames, two of which are legacy sub-frames 1131 andtwo of which are non-legacy sub-frames 1133. A UL portion of each radioframe includes four sub-frames, one of which is a legacy sub-frames 1141and three of which are non-legacy sub-frames 1143.

A second carrier 1120 that does not include legacy support, havingmultiple sub-carriers in a block of frequencies in the verticaldirection is illustrated over two successive 5 ms radio frames. A DLportion of each radio frame includes four sub-frames, all of which arenon-legacy sub-frames 1136. A UL portion of each radio frame includesfour sub-frames, all of which are non-legacy sub-frames 1146.

In the first carrier 1110, some sub-carriers of the legacy DL sub-frames1131 are allocated as guard tones 1135 between the sub-carriers of thefirst carrier 1110 and the sub-carriers of the second carrier 1120. Inthe second carrier 1120, no sub-carriers are allocated as guard tonesbetween the sub-carriers of the second carrier 1120 and the sub-carriersof the first carrier 1110.

In the first carrier 1110, some sub-carriers of the legacy UL sub-frames1141 are allocated as guard tones 1145 between the sub-carriers of thefirst carrier 1110 and the sub-carriers of the second carrier 1120. Inthe second carrier 1120, no sub-carriers are allocated as guard tonesbetween the sub-carriers of the second carrier 1120 and the sub-carriersof the first carrier 1110.

In a specific embodiment, for the case of 2 adjacent 5 MHz carriers,although the adjacent carriers are spaced by 5.25 MHz, there is nowasted bandwidth in between the carriers since the WiMAX OFDM numerologyuses over-sampling rate. The effective bandwidth for a 512-FFT is 5.6MHz. In some implementations, by adjusting the guard sub-carriers onboth sides, the gaps between two adjacent carriers can be removed.Furthermore, by adjusting the guard sub-carriers on both sides out-ofband spectrum mask requirements may also be met. This is illustrated inFIG. 12 a.

As shown in FIG. 12a , an uneven number of guard sub-carriers are usedon both sides of a carrier. A number of guard sub-carriers between twoadjacent carriers is 16 on each carrier. A number of guard sub-carriersat the edge of the spectrum is adjustable based on the spectrum maskrequirements.

There are two scenarios as illustrated in FIGS. 12a and 12b and FIGS.13a, 13b and 13 c.

Scenario 1—an Even Distance Between the Center Carrier Frequencies ofEach Carrier and the Spectrum Boundary

As shown in FIG. 12a and FIG. 12b , the center frequencies are 2.625 MHz(or 10.5 rasters) from the 5 MHz spectrum boundary. The drawback of thisscenario is the center frequency locations are not aligned with theraster boundaries.

Scenario 2—an Uneven Distance Between the Center Carrier Frequencies ofEach Carrier and the Spectrum Boundary

In scenario 2 center frequency locations are aligned with rasterboundaries. As shown in FIGS. 13a and 13b , the center frequency ofcarrier 1 is spaced 11 rasters from the 5 MHz spectrum boundary. Thecenter frequency of carrier 2 is spaced by 10 rasters from the 5 MHzspectrum boundary. This results in an uneven number of guardsub-carriers between two adjacent carriers. As shown in FIG. 13a , theguard sub-carriers on carrier 1 on the side that is next to carrier 2,is 5. The guard sub-carriers on carrier 2 on the side that is next tocarrier 1, is 28. The number of guard sub-carriers at the edge of thespectrum is adjustable based on the spectrum mask requirements.

FIG. 13c further shows a general case of more than two adjacentcarriers. The spacing of the center frequency from the spectrum boundaryis adjusted to ensure the center frequency is aligned with the rasterboundaries. In addition, the spacing between center frequencies ofadjacent carriers is maintained at 21 rasters.

In a specific embodiment that consists of a legacy WiMAX carrier, thecarrier frequency of the legacy carrier has to be centered in the 5 MHzband as shown FIG. 14. In this case the adjacent non-legacy carrier hasto be further offset in order to maintain the overall 5.25 MHz spacingbetween the center frequencies. As shown in FIG. 14, for the legacycarrier, a same number of guard sub-carriers are used on both sides ofthe carrier. For the non-legacy carrier, an uneven number of guardsub-carriers are used on both sides of a carrier. A number of guardsub-carriers on the side that is adjacent to the legacy carrier, is 5sub-carriers. A number of guard sub-carriers at the edge of the spectrumis adjustable based on the spectrum mask requirements. For othercarriers in the spectrum which are not adjacent to a legacy carrier, theapproaches described with reference to FIGS. 12a, 12b, 13a, 13b and 13c, may be used.

In some embodiments a method is provided to offset the spacing of thecenter frequencies of adjacent OFDM carriers to ensure the carrierspacing is divisible by the sub-carrier spacing.

In some embodiments a method is provided to offset the spacing of thecenter frequencies of adjacent OFDM carriers to have a spacing that isnot equal to the bandwidth of each carrier

In some embodiments a method is provided to allocate uneven number ofguard sub-carriers on both sides of the carrier

In some embodiments a method is provided to mix the regular carrier thathas same number of guard sub-carriers on both side of the carrier andhas center frequency located at the middle of the bandwidth, with acarrier that has uneven number of guard sub-carriers on both side of thecarrier and has center frequency that is offset of the middle of thebandwidth.

Description of Example Components of a Communication System

A high level overview of the mobile terminals 16 and base stations 14upon which aspects of the present invention are implemented is providedprior to delving into the structural and functional details of thepreferred embodiments. With reference to FIG. 15, a base station 14 isillustrated. The base station 14 generally includes a control system 20,a baseband processor 22, transmit circuitry 24, receive circuitry 26,multiple antennas 28, and a network interface 30. The receive circuitry26 receives radio frequency signals bearing information from one or moreremote transmitters provided by mobile terminals 16 (illustrated in FIG.1). A low noise amplifier and a filter (not shown) may co-operate toamplify and remove broadband interference from the signal forprocessing. Downconversion and digitization circuitry (not shown) willthen downconvert the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs) orapplication-specific integrated circuits (ASICs). The receivedinformation is then sent across a wireless network via the networkinterface 30 or transmitted to another mobile terminal 16 serviced bythe base station 14.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, and encodesthe data for transmission. The encoded data is output to the transmitcircuitry 24, where it is modulated by a carrier signal having a desiredtransmit frequency or frequencies. A power amplifier (not shown) willamplify the modulated carrier signal to a level appropriate fortransmission, and deliver the modulated carrier signal to the antennas28 through a matching network (not shown). Various modulation andprocessing techniques available to those skilled in the art are used forsignal transmission between the base station and the mobile terminal.

With reference to FIG. 16, a mobile terminal 16 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 14, the mobile terminal 16 will include a control system32, a baseband processor 34, transmit circuitry 36, receive circuitry38, multiple antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 14. A low noise amplifier and a filter (notshown) may co-operate to amplify and remove broadband interference fromthe signal for processing. Downconversion and digitization circuitry(not shown) will then downconvert the filtered, received signal to anintermediate or baseband frequency signal, which is then digitized intoone or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. The baseband processor 34 is generallyimplemented in one or more digital signal processors (DSPs) andapplication specific integrated circuits (ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 40 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are used for signal transmission between themobile terminal and the base station.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation utilizes the performance of an Inverse Fast FourierTransform (IFFT) on the information to be transmitted. For demodulation,the performance of a Fast Fourier Transform (FFT) on the received signalrecovers the transmitted information. In practice, the IFFT and FFT areprovided by digital signal processing carrying out an Inverse DiscreteFourier Transform (IDFT) and Discrete Fourier Transform (DFT),respectively. Accordingly, the characterizing feature of OFDM modulationis that orthogonal carrier waves are generated for multiple bands withina transmission channel. The modulated signals are digital signals havinga relatively low transmission rate and capable of staying within theirrespective bands. The individual carrier waves are not modulateddirectly by the digital signals. Instead, all carrier waves aremodulated at once by IFFT processing.

In operation, OFDM is preferably used for at least down-linktransmission from the base stations 14 to the mobile terminals 16. Eachbase station 14 is equipped with “n” transmit antennas 28, and eachmobile terminal 16 is equipped with “m” receive antennas 40. Notably,the respective antennas can be used for reception and transmission usingappropriate duplexers or switches and are so labelled only for clarity.

With reference to FIG. 17, a logical OFDM transmission architecture willbe described. Initially, the base station controller 10 will send datato be transmitted to various mobile terminals 16 to the base station 14.The base station 14 may use the channel quality indicators (CQIs)associated with the mobile terminals to schedule the data fortransmission as well as select appropriate coding and modulation fortransmitting the scheduled data. The CQIs may be directly from themobile terminals 16 or determined at the base station 14 based oninformation provided by the mobile terminals 16. In either case, the CQIfor each mobile terminal 16 is a function of the degree to which thechannel amplitude (or response) varies across the OFDM frequency band.

Scheduled data 44, which is a stream of bits, is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 46. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 48. Next, channel coding is performed using channelencoder logic 50 to effectively add redundancy to the data to facilitaterecovery and error correction at the mobile terminal 16. Again, thechannel coding for a particular mobile terminal 16 is based on the CQI.In some implementations, the channel encoder logic 50 uses known Turboencoding techniques. The encoded data is then processed by rate matchinglogic 52 to compensate for the data expansion associated with encoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. Preferably,Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key(QPSK) modulation is used. The degree of modulation is preferably chosenbased on the CQI for the particular mobile terminal. The symbols may besystematically reordered to further bolster the immunity of thetransmitted signal to periodic data loss caused by frequency selectivefading using symbol interleaver logic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 60, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 16. The STC encoder logic60 will process the incoming symbols and provide “n” outputscorresponding to the number of transmit antennas 28 for the base station14. The control system 20 and/or baseband processor 22 as describedabove with respect to FIG. 15 will provide a mapping control signal tocontrol STC encoding. At this point, assume the symbols for the “n”outputs are representative of the data to be transmitted and capable ofbeing recovered by the mobile terminal 16.

For the present example, assume the base station 14 has two antennas 28(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT processor 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT processors 62 will preferablyoperate on the respective symbols to provide an inverse FourierTransform. The output of the IFFT processors 62 provides symbols in thetime domain. The time domain symbols are grouped into frames, which areassociated with a prefix by prefix insertion logic 64. Each of theresultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUC) and digital-to-analog (D/A)conversion circuitry 66. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 68 and antennas 28. Notably, pilotsignals known by the intended mobile terminal 16 are scattered among thesub-carriers. The mobile terminal 16, which is discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 18 to illustrate reception of thetransmitted signals by a mobile terminal 16. Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile terminal16, the respective signals are demodulated and amplified bycorresponding RF circuitry 70. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (A/D) converter and down-conversion circuitry72 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGC) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic 76,which includes coarse synchronization logic 78, which buffers severalOFDM symbols and calculates an auto-correlation between the twosuccessive OFDM symbols. A resultant time index corresponding to themaximum of the correlation result determines a fine synchronizationsearch window, which is used by fine synchronization logic 80 todetermine a precise framing starting position based on the headers. Theoutput of the fine synchronization logic 80 facilitates frameacquisition by frame alignment logic 84. Proper framing alignment isimportant so that subsequent FFT processing provides an accurateconversion from the time domain to the frequency domain. The finesynchronization algorithm is based on the correlation between thereceived pilot signals carried by the headers and a local copy of theknown pilot data. Once frame alignment acquisition occurs, the prefix ofthe OFDM symbol is removed with prefix removal logic 86 and resultantsamples are sent to frequency offset correction logic 88, whichcompensates for the system frequency offset caused by the unmatchedlocal oscillators in the transmitter and the receiver. Preferably, thesynchronization logic 76 includes frequency offset and clock estimationlogic 82, which is based on the headers to help estimate such effects onthe transmitted signal and provide those estimations to the correctionlogic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 90. Theresults are frequency domain symbols, which are sent to processing logic92. The processing logic 92 extracts the scattered pilot signal usingscattered pilot extraction logic 94, determines a channel estimate basedon the extracted pilot signal using channel estimation logic 96, andprovides channel responses for all sub-carriers using channelreconstruction logic 98. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. Examples ofscattering of pilot symbols among available sub-carriers over a giventime and frequency plot in an OFDM environment are found in PCT PatentApplication No. PCT/CA2005/000387 filed Mar. 15, 2005 assigned to thesame assignee of the present application. Continuing with FIG. 18, theprocessing logic compares the received pilot symbols with the pilotsymbols that are expected in certain sub-carriers at certain times todetermine a channel response for the sub-carriers in which pilot symbolswere transmitted. The results are interpolated to estimate a channelresponse for most, if not all, of the remaining sub-carriers for whichpilot symbols were not provided. The actual and interpolated channelresponses are used to estimate an overall channel response, whichincludes the channel responses for most, if not all, of the sub-carriersin the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 100, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 100 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols

The recovered symbols are placed back in order using symbolde-interleaver logic 102, which corresponds to the symbol interleaverlogic 58 of the transmitter. The deinterleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 104. The bits are then de-interleaved using bit de-interleaverlogic 106, which corresponds to the bit interleaver logic 54 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 108 and presented to channel decoder logic 110 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 112 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 114 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 116.

In parallel to recovering the data 116, a CQI, or at least informationsufficient to create a CQI at the base station 14, is determined andtransmitted to the base station 14. As noted above, the CQI may be afunction of the carrier-to-interference ratio (CR), as well as thedegree to which the channel response varies across the varioussub-carriers in the OFDM frequency band. The channel gain for eachsub-carrier in the OFDM frequency band being used to transmitinformation is compared relative to one another to determine the degreeto which the channel gain varies across the OFDM frequency band.Although numerous techniques are available to measure the degree ofvariation, one technique is to calculate the standard deviation of thechannel gain for each sub-carrier throughout the OFDM frequency bandbeing used to transmit data.

FIGS. 1 and 15 to 18 each provide a specific example of a communicationsystem or elements of a communication system that could be used toimplement embodiments of the invention. It is to be understood thatembodiments of the invention can be implemented with communicationssystems having architectures that are different than the specificexample, but that operate in a manner consistent with the implementationof the embodiments as described herein.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practised otherwise than as specifically described herein.

The invention claimed is:
 1. A user equipment (UE), comprising: abaseband processor; one or more antennas; transmit circuitry coupled tothe baseband processor and the one or more antennas; and receivecircuitry coupled to the baseband processor and the one or moreantennas; wherein the baseband processor is configured to cause the UEto: for multi-carrier configurations communication with a base station,receive on two or more carriers of a plurality of carriers, wherein eachcarrier of the plurality of carriers is aligned with a respectivefrequency raster location, wherein respective frequency raster locationsof adjacent carriers are separated by integer multiples of a definedfrequency raster size, wherein the defined frequency raster size is notdivisible by a defined subcarrier spacing an integer number of times,and wherein spacing between adjacent carriers of the two or morecarriers is divisible an integer number of times by each of the definedsubcarrier spacing and the defined frequency raster size.
 2. The UE ofclaim 1, wherein bandwidths of the two or more carriers of the pluralityof carriers are each integer multiples of a defined frequency rastersize and not integer multiples of the defined subcarrier spacing.
 3. TheUE of claim 1, wherein spacing of center frequencies of adjacentcarriers of the two or more carriers is not equal to a carrier bandwidthfor either carrier.
 4. The UE of claim 1, wherein there is an unevenspacing between center carrier frequencies of each carrier of theadjacent carriers of the two or more carriers and a spectrum boundarybetween the adjacent carriers.
 5. The UE of claim 1, wherein a centerfrequency of each carrier of the adjacent carriers of the two or morecarriers is separated by an integer multiple of the frequency rastersize; and wherein the subcarrier spacing is the subcarrier spacing in anorthogonal frequency division multiplexing (OFDM) transmission scheme.6. The UE of claim 1, wherein an uneven number of guard subcarriers areallocated on either side of a carrier of the adjacent carriers of thetwo or more carriers.
 7. The UE of claim 1, wherein for other carriersof the plurality of carriers not part of the multi-carrierconfigurations, spacing of the center frequencies of carriers isdivisible an integer number of times by a defined center frequencyraster, but not by the defined subcarrier spacing.
 8. A user equipment(UE), comprising: a baseband processor; one or more antennas; transmitcircuitry coupled to the baseband processor and the one or moreantennas; and receive circuitry coupled to the baseband processor andthe one or more antennas; wherein the baseband processor is configuredto cause the UE to: receive frequency adjacent first and second carriersaccording to a multiple carrier configuration in a portion of downlinksubframes, wherein the first carrier is received at a first frequencylocation aligned with a first frequency raster location, wherein thesecond carrier is received at a second frequency location aligned with asecond frequency raster location, wherein carrier spacing of the firstand second carriers is given by first and second frequency rasterlocations, respectively, and is divisible an integer number of times ofa defined frequency raster and a defined subcarrier spacing; and whereinbandwidths of the first and second carriers are each integer multiplesof a defined frequency raster size and not integer multiples of thedefined subcarrier spacing, wherein the defined frequency raster size isnot divisible by the defined subcarrier spacing an integer number oftimes, and wherein the defined subcarrier spacing is a subcarrierspacing in an orthogonal frequency division multiplexing (OFDM)transmission scheme.
 9. The UE of claim 8, wherein spacing of the centerfrequencies of the first and second carriers is not equal to a carrierbandwidth for either carrier.
 10. The UE of claim 8, wherein there is anuneven spacing between center carrier frequencies of each carrier of thefirst and second carriers and a spectrum boundary between the first andsecond carriers.
 11. The UE of claim 8, wherein a center frequency ofeach of the first and second carriers is separated by an integermultiple of a frequency raster size.
 12. The UE of claim 8, whereinthere are no guard subcarriers between adjacent carriers beyond acarrier bandwidth for each of the first and second carriers.
 13. The UEof claim 8, wherein an uneven number of guard subcarriers are allocatedon either side of one of the first and second carriers.
 14. The UE ofclaim 8, wherein for other carriers not part of a multi-carrierconfiguration, spacing of the center frequencies of carriers isdivisible an integer number of times by a defined center frequencyraster, but not by the defined subcarrier spacing.
 15. A method ofspacing carriers by a user equipment (UE), comprising: receiving aplurality of carriers for communication with a plurality of mobilestations, wherein each carrier of the plurality of carriers is alignedwith a respective frequency raster location, wherein respectivefrequency raster locations of adjacent carriers are separated by integermultiples of a defined frequency raster size, and wherein the definedfrequency raster size is not divisible by a defined subcarrier spacingan integer number of times; and for multi-carrier configurationscommunication with at least one mobile station of the plurality ofmobile stations, receiving on two or more carriers of the plurality ofcarriers, wherein spacing of the respective frequency raster locationsof adjacent carriers of the two or more carriers is divisible an integernumber of times by each of the defined subcarrier spacing and thedefined frequency raster size.
 16. The method of claim 15, whereinspacing of center frequencies of adjacent carriers of the two or morecarriers is not equal to a carrier bandwidth for either carrier.
 17. Themethod of claim 15, wherein there is an uneven spacing between centercarrier frequencies of each carrier of the adjacent carriers of the twoor more carriers and a spectrum boundary between the adjacent carriers.18. The method of claim 15, wherein a center frequency of each carrierof the adjacent carriers of the two or more carriers is separated by aninteger multiple of the frequency raster size; and wherein thesubcarrier spacing is the subcarrier spacing in an orthogonal frequencydivision multiplexing (OFDM) transmission scheme.
 19. The method ofclaim 15, wherein there are no guard subcarriers between the adjacentcarriers of the two or more carriers beyond a carrier bandwidth.
 20. Themethod of claim 15, wherein an uneven number of guard subcarriers areallocated on either side of each carrier of the adjacent carriers of thetwo or more carriers.